The bridging sheet in HIV-1 gp120 connects the inner domain with the outer domain of gp120. Half of the bridging sheet ([unreadable]2/3) is composed of amino acids from the variable segments from the V2 and V3 domains whereas the second half of the bridging sheet, referred to as [unreadable]20/21, is composed of highly conserved amino acids from the C4 domain. [unreadable]20/21 is a major component of the CD4 binding site (CD4bs) in gp120 and, when it is not occupied by CD4, appears to be accessible to binding antibodies. Within the first 3 to 4 months of HIV infection, antibodies to the conformationally constrained [unreadable]20/21 are not produced, making [unreadable]20/21 a possible target for early stage therapeutic vaccine intervention. We have successfully designed and synthesized an immunogen from the [unreadable]20/21 amino acid sequence, called CDC4, and immunized test animals to evaluate the targeted antibodies for effectiveness in binding to gp120 from various strains of the virus. The aim is to develop CDC4 as a component of a therapeutic vaccine for suppressing the spread of HIV in vivo. The goal of this proposal is to tag with antibodies the [unreadable]20/21 portion of the bridging sheet expressed on the surface of HIV-infected cells. In vitro neutralization assays and tests with the antibodies capable of activating antibody-dependent cellular cytotoxicity (ADCC) as a possible correlate of in vivo neutralization will be performed. Simple binding of anti- [unreadable]20/21 antibodies to gp120 and activating ADCC-like mechanisms then might act to control viral spread and perhaps delay the need of an infected patient having to take anti HIV-1 drugs. PUBLIC HEALTH RELEVANCE: This project is geared toward creating a novel therapeutic vaccine against a conserved sites on the surface of HIV-1. Such a novel immunotherapeutic should be useful in assisting patients suffering from HIV infection with keeping the virus under control.